1. Field of the Invention
The present invention relates to an intermittent operative communication apparatus and a method therefor, and more particularly to an intermittent communication apparatus for use in a telecommunications network, such as a sensor network, formed by a plurality of wireless communication nodes located spatially apart from each other to perform data communication with each other via wireless transmission.
2. Description of the Background Art
For a plurality of wireless communication nodes performing data communication with each other via wireless transmission media, a communication method with intermittent operation is researched and developed in which, for power saving, a device not regularly used is turned off so as to intermittently operate. A communication scheme with intermittent operation is taught by En-Yi A. Lin, et al., “Power-Efficient Rendez-vous Schemes for Dense Wireless Sensor Networks”, IEEE International Conference on Communications 2004, Paris, France, June 2004.
First with reference to FIG. 8, the communication method disclosed by Lin, et al., will be described. The method taught by Lin, et al., is to regularly power on a wireless device only for a short period of time to wait for reception of a signal, and, for the remaining period of time, to power off the wireless device, thus contemplating power saving. In the context, the timing for such a regular waiting for signal reception is called sniff timing.
In order to transmit a data packet to a wireless node that performs power saving operation with the above way of intermittent reception, a packet has to be transmitted in time with a short reception waiting interval. It is however difficult to identify such timing from external nodes. The system is thus adapted to consecutively transmit control packet for start requests when a send packet is generated. Such consecutive transmission of start packets may cause one of the start packets to be received by a destination node sooner or later at its reception wait timing. In response to the start request, the receiving node will return a start response to thereby notify the sending node of having entered its reception waiting state. The sending node will, after having received the start response, transmit the data packet. Thus, the sending state can normally be established. This scheme is called the power saving listening, a very simple way to accomplish an effective power saving.
However, in the method disclosed by Lin, et al., if the nodes operate at the operational interval T and randomly determine the sniff timing thereof, then control packet for start requests when sending a data packet to some node will be transmitted consecutively at the timing, which is averaged to a value of T/2. This means that packets are relayed with a delay caused which is in average equal to the interval of T/2. For effective power saving, some length of operational interval T is required. However, the longer operational interval, the longer delay. Thus, in an application having the delay restricted, a longer operational interval is not allowed, causing a problem that the power saving cannot fully be effected.